Definitely not. Consumers are best served when you have a bunch of relatively equal players competing for their business, and where success is rewarded financially. That gives everybody an incentive to focus on continuously getting better at serving the customer through R&D, etc.
But if the reward for success is just having Amazon come in and hoover up the money you would have gotten by launching a knockoff, then suddenly there's a lot less incentive to invest in novel products. That's true both for categories where Amazon is competing and ones where it isn't currently.
I wouldn't be surprised if Amazon's replacement product is sometimes modestly worse, because a) they don't have the kind of deep expertise in a product that the original creators do, and b) it doesn't have to be as good to get the money.
And then there's after-sale support. Amazon's customer support is atrocious. The one thing they're good at is taking things back. But anything more complex and it's a nightmare.